1. Field of the Invention
This invention relates to video recording apparatus and methods and, more particularly, to particular methods and apparatus for improving the density and fidelity of video recording.
2. Description of the Prior Art
Substantial time and effort have been invested in attempts to realize a satisfactory, commercially feasible video recording and playback system. Ideally, such system should be analogous to the cassette type recorders and players available in the audio recording/playback field. In those video recording and playback systems which have been or are now on the market in limited quantities, various types of record media have been employed, such as tapes, tape cassettes, discs, magnetic cards, and the like. Within the broad spectrum of video recording and playback systems is a more specialized segment of the market involving the playback of pre-recorded video programs. In all of the consumer-directed video recording and/or playback systems, it is virtually essential to provide at least 30 minutes of recording time and preferably one hour or more. This presents extreme demands on video recording and playback systems and the associated record media, since a great deal of information must be recorded, requiring very high recording density with significant fidelity.
Disclosures of particular prior art video recording and playback systems of the general type to which the present invention is directed may be found in U.S. Pat. Nos. 3,911,483 of Kihara et al and 3,701,846 of Zenzefilis, the applicant herein. In the system of the latter patent, a specialized type of phase modulation is employed referred to as pulse length code (PLC) or pulse width modulatin (PWM). In the Kihara et al patent, the disclosed system utilizes a more conventional type of phase modulation. In both prior art systems, increased recording density without cross talk is possible through track overlap by virtue of the alignment of corresponding picture elements from track to track at the same relative positions along the tracks. In both systems, the path of the transducer relative to the record medium, considered for simplicity stationary for a moment, is a relatively straight line with movement directed more or less orthogonally to the direction of the tracks. This imposes certain limitations on the recorded information and also requires a very precise drive mechanism for relative transducer movement. One of the problems encountered heretofore in recording systems of the type referred to above as well as those of more general application, such as in digital recordings in computer peripheral systems and the like, has been a certain inherent longitudinal motion of the recording and reproducing transducers known as "head jitter". This imposes a requirement for providing certain minimum positional tolerances for the service and clock transducers in order to prevent improper phase information developing from unacceptable relative displacement of those transducers.
Although increased density in video recording may be achieved by developing track overlap with reproduction by transducers scanning more than one track simultaneously in the manner followed by the systems of the above cited patents without objectionable cross talk, the accompanying sound recording cannot be treated the same way because of differences in the video and sound information content and in the respective perception functions. The cited Zenzefilis patent discloses a sound recording technique which is directed to obviating the problem of cross talk in overlapping sound tracks. In the disclosed system, as an example, only every fourth sync. interval is modulated with audio. While this solves the problem described to some extent and permits playback without objectionable cross talk for transducers overlapping tracks to a certain degree, it still imposes a limitation with respect to the extent of track overlap that is permissible for a given transducer-to-track width ratio, and also a limitation of the upper frequency response of the sound reproduction.
It is, therefore a general object of the present invention to provide improvements in previously known video-with-sound recording systems which achieve enhanced operational performance with increased recording density, reliability, simplicity, and fidelity.